fix: preserve reasoning capabilities for routed model aliases

[xhwxt]

Summary

• Read reasoning capabilities from inline model_providers.*.models[] definitions in the Codex config.
• Resolve routed aliases through model, id, slug, and upstreamModel identifiers.
• Preserve supported efforts, defaults, upstream parameter mappings, and provider-config provenance in the generated model catalog.
• Add coverage for an alias whose reasoning metadata exists only on the upstream model definition.

Validation

• git diff --check
• Python reasoning-guard syntax and smoke tests
• Rust tests/build not run locally because the Rust toolchain is unavailable in this environment.